Asking for extra money

I am a regular on the Bolt App, recently I have been noticing when you request, a driver will accept, call you and ask how much is the ride, he will then tell you if you 'top' him up with an extra R30/R40 he will come through, this has happened several times, lots of people are complaining about this operandi, also if a driver comes to fetch you, he will ask you if you have a promo, if you say yes, they tell you they don't do promo rides and drive off.